One means for detecting a damage in a wire rope or a break in an element wire is a wire rope flaw detector as described in PTL 1 which uses a permanent magnet or electromagnet to magnetize a predetermined axial section of a wire rope that runs at a constant speed and uses a magnetic sensor placed in the predetermined section to detect a leakage flux leaking from a damaged area of the wire rope.
In such a wire rope flaw detector, a coil is employed as a magnetic sensor for detecting a leakage flux, which is formed generally U-shaped so as to surround almost a half circumference of a wire rope.
Furthermore, a protection plate made of a non-magnetic material having a capability of protecting the coil from the sliding of the rope, and a pole piece of a ferromagnetic material that is positioned between the permanent magnet and the wire rope while supporting the protection plate and that reduces the magnetoresistance between the permanent magnet and the wire rope are also formed so as to have a generally U-shaped cross section, all of which are integrated to form a probe.
The PTL 1 also has suggested a structure in which a magnetizer composed of a permanent magnet (or electromagnet) and a back yoke can be separated from the probe.
This structure may be because, since the cross section of the probe is generally U-shaped with a particular radius, a probe having a generally U-shaped cross section with a different radius needs to be used as appropriate for a wire rope having a different diameter.